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I would like to build a low-cost home UV exposure box for PCB manufacturing. Recently my attention was brought to these dirt cheap UV bulbs which are used in manicure drying lamps. I have the ballast of a 32W CFL tube which I would like to use for the task. I have a couple of questions:

  • How many tubes should I use with the 32W ballast?
  • How should I wire the tubes? I'm guessing in series, since the ballast is supposed to be a constant-current source; am I right?
  • The ballast has 4 electrodes, but the UV tubes have only 2. I'm guessing it's because the electrodes in the UV tubes don't have to be heated. What should I do with the extra wires? Short them like this? Won't it melt the heating circuitry then?
  • Will this expose the PCB adequately?
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    \$\begingroup\$ "Does not contain mercury"? Do they run on pixie dust? You should probably use ballasts designed for that size of 9W visible bulb rather than trying to match random bits to each other. \$\endgroup\$ – Spehro Pefhany Jun 26 '15 at 13:40
  • \$\begingroup\$ As I found out in the meantime, these probably have some kind of internal igniter circuitry to heat up the electrodes. As for the "no mercury" part, mercury vapor is not the only gas that can generate light - maybe they use some kind of noble gas. Or unicorn fart, who knows? I could use proper ballast for this, but it would make it expensive. I also could do it the proper way and have my PCBs done in a fab house, or just buy the gadget I wanted to make - but then the whole procedure just turns into shopping and stops being a hobby. Where's the fun in that? Also money's kind of a factor here. \$\endgroup\$ – matega Jun 26 '15 at 18:31
  • \$\begingroup\$ If the ballast is the instant-start type it may be able to produce enough voltage to work with 4 tubes in series. There is no circuitry inside the bulbs- it's the type of ballast. If the ballast has heater outputs, you're probably scuppered. Of course there is always the possibility something bad would happen even if appears to work, so E&OE. They definitely contain a bit of mercury vapor- the seller is ignorant and/or lying. \$\endgroup\$ – Spehro Pefhany Jun 26 '15 at 18:42
  • \$\begingroup\$ By far my favorite part about these bulbs is the fact they are labeled as UV and then in the description itself it says they are white light and no UV or IR light emitted \$\endgroup\$ – Dave Dec 25 '15 at 8:06
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This is a UV B (365nm) lamp with two pins. A bi-pin tube is designed for conventional (inductive) ballast and is incompatible with electronic ballasts. Internally it has a capacitor that acts as built-in starter.

You can connect it with single ballast rated at approx 9W (usually one ballast covers range from 5 to 11W). In your case you would have to connect 3 or 4 bulbs in parallel (ballast is a current shift component) and ballast in series. However if the ballast has 4 pins it means it's designed for 2 x 16W load, so you could connect just two bulbs to one terminal (this is close to 18W). You should check (with ohmmeter) if there are actually two coils inside. Connecting four lamps will slightly overload it (you would need a 36W ballast for that).

Personally I would try connecting two bulbs in parallel and then hook those to one half of the ballast (ballast goes in series with the bulbs). This would give the current flowing thru the bulbs a proper cos(fi) and keep the load on the ballast under 20W.

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I spent a day faffing with these tubes. They need a 9W (5-11W) ballast for each and an external starter as they do not have one in the white box section. I discovered this by cutting one up!

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